The present invention relates to control means for commutatorless motor for driving the synchronous motor by the thyristor frequency converter.
As is well known in the art, the commutatorless motor is a commutatorless variable speed motor consisting of a combination of a synchronous motor and frequency converter consisting of a thyristor for electrically controlling the synchronous motor. This commutatorless motor has features that its control range is very extensive and also that its maintenance and inspection are easy since it is free from commutator and brushes.
In this type of commutatorless motor, the power-factor varies with increase of load, and also the armature terminal voltage is changed. From this ground the capacity of the frequency converter and the synchronous motor are increased.
In order to compensate for the effect of the armature reaction, it is usual to adopt a method, in which a compensating winding for producing an electromotive force at right angles to the electromotive force of the field winding is provided and current of a magnitude corresponding to the armature current is caused to pass through the compensating winding. However, by providing the compensating winding the size of the field side of the motor is increased, and also a control circuit for controlling the current caused through the compensating winding is required. Therefore, increase of the size and cost of the commutatorless motor system is inevitable.
Meanwhile, with recent trend for adopting commutatorless motors in various fields in rollers and fans, it has been strongly desired to be able to simply compensating the armature reaction.